冰煤断裂韧度的测试研究

通过对冰煤在-30℃低温状态下的断裂韧度K_IC的测试试验, 得出了在不同预制裂纹长度条件下冻结煤体的断裂韧度变化情况. 试验中制备了三点弯曲试样并制作了低温环境下的三点弯曲实验装置, 对冰煤的试样制备、试验装置、 K_IC计算公式以及裂纹尖端塑性区的大小等断裂力学问题进行探讨, 并且对试样尺寸的有效性进行了验证. 结果表明, 断裂韧度K_IC与裂纹深度a/W的变化方向相反, a/W越大, K_IC越小, 此时裂纹越易开裂.

Experimental Study of the Fracture Toughness of Frozen Coal

Coal is always frozen into block with water in transportation for the purpose of being fixed up and not burned. As a sort of multiple components and a granule aggregation in dispersed state, frozen coal behaves similar to frozen soil. On the basis of its unique ice-cementation effect and the existent of non-frozen water that varies with dynamical balance state between the frameworks of mineral granule, the mechanical behaviour of frozen coal is more complex than usual incompact medium, dependent on load, vibration period and temperature. In order to make it easy to unpack frozen coal, people prefabricate some cracks on it before transportation. In this thesis, experimental study of fracture toughness of frozen coal at low temperature is presented. Three-point bending tests are conducted on frozen coal so as to determine its fracture toughness K-{IC} under various crack length. Sample dimension must meet three essential conditions: plane strain condition, linear elasticity condition and ligament size condition. After the tests, K-{IC} was calculated from the test data, which should be taken take into account with the three essential conditions to validate the validity of the test. The test results show that the value of K-{IC} of frozen coal decreases with shortening the crack length. Thus the crack should be prefabricated deep customarily. But due to vibration action from the carriage, the crack may be getting deeper. So under vibration action, the depth of crack should be prefabricated equal to the reality. Sample preparing, test equipment construction, calculation formula of K-{IC}, of plastic area in crack peak, phenomena of inactivation and development of crack are also discussed.